The invention relates to a magnetic clutch and brake assembly for selectively coupling a driven gear to either a power input idler gear, or to positively secure the rotatable gear in a braked position. More particularly, the invention relates to a clutch and brake assembly that is useful in driving and controlling the position of rotatable instrument indicating dials such as the decade gear driven indicating pointers commonly employed on electrical power measuring meters.
A wide variety of magnetic clutch and brake mechanisms are generally well-known in the prior art. An example of a relatively recently developed magnetic clutch and brake mechanism that has been used successfully in conjunction with an electric meter dial drive is described in U.S. Pat. No. 4,050,020, which issued on Sept. 20, 1977 and is assigned to the assignee of the present invention. In fact, the unique features of the present invention involve improvements that can readily be made in the type of magnetic clutch and brake mechanism disclosed in that earlier patent.
As a consequence of operating experience with the type of magnetic clutch and brake assembly disclosed in that patent, it was discovered that many electric meter applications demand the provision of the more positive driving and braking actions than are provided by that magnetic clutch and brake mechanism. The mechanism described in that patent depends solely on friction and magnetic coupling between its relatively movable components to afford desired clutching and braking functions. Accordingly, the torque capability of the device is limited to the holding strength of the combined friction and magnetic forces between two sliding clutch surfaces. Although under most normally encountered meter operating conditions little or no slippage does, in fact, occur between either the clutch or the magnetic brake of those mechanisms, field experience has shown that undesirable slippage will occur in those few applications where the meter is subject to excessive vibration. Of course, when such slippage occurs, which the shiftable magnetic member of such a clutch and brake assembly in either its driving or braking mode, some error is introduced in the meter dial readings. The slippage either reflects relative movement of the indicating input gear train, which is not recorded on the movable dials of the meter register, or it may represent random error in either an up-scale or down-scale movement of the register dial due to random movement induced in the dials by vibration and rotation of the dial gear train when it is supposed to be held securely in a braked position. In order to avoid such undesirable errors in resultant meter readings, it is necessary to improve the type of magnetic clutch and brake mechanism described in the foregoing patent by incorporating an economically feasible positive driving and braking means in it.
Accordingly, it is a primary object of the present invention to overcome the above-noted disadvantages of known types of magnetic clutch and brake mechanisms by providing an accurate, and economical to manufacture, clutch and brake assembly that is free of such shortcomings.
Another object of the invention is to provide a magnetic clutch and brake assembly that has a positive, high torque drive coupling and brake mechanism that prevents more than a predetermined minimum angular degree of slippage between a shiftable magnetic member and associated idler gear and braking post.
Yet another object of the invention is to provide an alternative drive coupling between a shiftable magnetic member of a magnetic clutch assembly that is operable to enable the magnetic member and clutch assembly to engage one another in driving relationship without requiring a positive drive coupling between the members to be engaged in its positive driving relationship.
A still further object of the invention is to provide a magnetic braking assembly with a positive brake means that mechanically prevents more than a predetermined degree of angular rotation of a shiftable magnetic member after it is moved to its braked position even when the mechanism is subjected to substantial mechanical vibration.
Additional objects and advantages of the invention will be apparent to those skilled in the art from the description of it presented herein considered in conjunction with the accompanying drawings.